In, for instance, the transport of a load on a fluid cushion it is necessary to pull in or pay out a cable or the like attached to the load but it is impossible to wind this element around a drum. Instead the cable must pass under tension straight through the cable mover.
Such a mover is known which has a normally horizontal lever pivotal about a horizontal transverse axis on a fixed support and having two attachments flanking the pivot. Arms pivoted on the attachments each carry a pair of jaws between which the cable passes, and which automatically lock on and grip the cable when pulled up along it in one direction, but which slide in the other direction. Thus as the lever is rocked back and forth about its axis the cable is first gripped and lifted by one of the grippers while the other slides down it, and then is clenched by the other gripper as it lifts while the one gripper slides down the cable to start lifting again. With a long lever arm the system can exert enormous forces, and can be operated by a crank or hydraulic cylinder for nonmanual operation.
Such an arrangement advances the cable and its load in steps. This jerky advance frequently damages the load itself, and subjects the cable to peak loads well in excess of the actual mass being lifted. The concentrated gripping force at one location is compounded by the start-and-stop advance often causing whichever set of grippers is active to bite into and damage the cable. It is also standard that such devices are only capable of hauling the cable with great force in one direction and in the opposite paying-out direction are relatively weak.